The Supreme Court has struck down an Arizona law requiring residents to show identification in order to register to vote.

The 7-2 ruling issued Monday said Arizona is not authorized to make changes to federal voter registration requirements, an action that could have consequences on a number of other states. Liberals had fought for the Supreme Court to overturn the law, which they believed restricted mostly poor, minority voters from reaching the polls.

Four states — Alabama, Georgia, Kansas, and Tennessee — also required proof of citizenship for residents looking to register.

Even traditionally conservative Justice Antonin Scalia voted against the law, writing in his decision that Arizona’s proof of citizenship requirement ushered in by voters in 2004 went against the 1993 federal law making it easier to register to vote. Scalia did appear to show sympathy for the state but said it must take a different approach than changing a federal law without approval.

Federal voter registration law requires registrants to claim citizenship under penalty of perjury, but Arizona required a separate prof of citizenship.

Justice Clarence Thomas, who dissented, said the Constitution did allow for Arizona’s action.

“I would construe the (federal) law as only requiring Arizona to accept and use the form as part of its voter registration process, leaving the state free to request whatever additional information it determines is necessary,” Thomas said.

The Supreme Court’s decision to overturn Arizona’s voter registration law was met with praise by voting rights groups.

“Today’s decision sends a strong message that states cannot block their citizens from registering to vote by superimposing burdensome paperwork requirements on top of federal law,” said Nina Perales of the Mexican American Legal Defense and Educational Fund, which worked on a case against the Arizona law.